arXiv subjects

Z. Jiang

Publications and source records attributed to Z. Jiang.

78 records · Page 5Linked to original sources

arXiv2005

Thermal conductance of Andreev interferometers

We calculate the thermal conductance $G^T$ of diffusive Andreev interferometers, which are hybrid loops with one superconducting arm and one normal-metal arm. The presence of the superconductor suppresses $G^T$; however, unlike a conventional superconductor, $G^T/G^T_N$ does not vanish as the temperature $T\to0$, but saturates at a finite value that depends on the resistance of the normal-superconducting interfaces, and their distance from the path of the temperature gradient. The reduction of $G^T$ is determined primarily by the suppression of the density of states in the proximity-coupled normal metal along the path of the temperature gradient. $G^T$ is also a strongly nonlinear function of the thermal current, as found in recent experiments.

cond-mat.mes-hall↗

arXiv2005

Quantitative measurements of the thermal resistance of Andreev interferometers

Using a local thermometry technique, we have been able to quantitatively measure the thermal resistance $R^T$ of diffusive Andreev interferometers. We find that $R^T$ is strongly enhanced from its normal state value at low temperatures, and behaves non-linearly as a function of the thermal current through the sample. We also find that the $R^T$ oscillates as a function of magnetic flux with a fundamental period corresponding to one flux quantum $Φ_0=h/2e$, demonstrating the phase coherent nature of thermal transport in these devices. The magnitude of $R^T$ is larger than predicted by recent numerical simulations.

cond-mat.mes-hall↗

arXiv2004

Magnetization Losses in Multifilament Coated Superconductors

We report the results of a study of the magnetization losses in experimental multifilament, as well as control (uniform), coated superconductors exposed to time-varying magnetic field of various frequencies. Both the hysteresis loss, proportional to the sweep rate of the applied magnetic field, and the coupling loss, proportional to the square of the sweep rate, have been observed. A scaling is found that allows us to quantify each of these contributions and extrapolate the results of the experiment beyond the envelope of accessible field amplitude and frequency. The combined loss in the multifilament conductor is reduced by about 90% in comparison with the uniform conductor at full field penetration at sweep rate as high as 3T/s.

cond-mat.supr-con↗

arXiv2003

Novel pinning phenomena in a superconducting film with a square lattice of artificial pinning centers

We study the transport properties of a superconducting Nb film with a square lattice of artificial pinning centers (APCs) as a function of dc current, at a temperature close to the superconducting transition temperature of the film. We find that, at low dc currents, the differential resistance of the film shows the standard matching field anomaly, that is, the differential resistance has a local minimum at magnetic fields corresponding to an integer number of flux lines per APC. However, at higher dc currents, the differential resistance at each matching field turns to a local maximum, which is exactly opposite to the low current behavior. This novel effect might indicate that the flux lines in the APC system change their flow mode as the dc current is increased.

cond-mat.mes-hall↗

arXiv2002

Local thermometry technique based on proximity-coupled superconductor/normal-metal/superconductor devices

In mesoscopic superconductor/normal-metal/superconductor (SNS) heterostructures, it is known that the resistance of the normal metal between the superconductors has a strong temperature dependence. Based on this phenomenon, we have developed a new type of thermometer, which dramatically enhances our ability to measure the local electron temperature Te at low temperatures. Using this technique, we have been able to measure small temperature gradients across a micron-size sample, opening up the possibility of quantitatively measuring the thermal properties of mesoscopic devices.

cond-mat.mes-hall↗

arXiv1995

Study of Oxygen Diffusion and Clustering in Silicon using an Empirical Interatomic Potential

The diffusion path and diffusivity of oxygen in crystalline silicon are computed using an empirical interatomic potential which was recently developed for modelling the interactions between oxygen and silicon atoms. The diffusion path is determined by constrained energy minimization, and the diffusivity is computed using jump rate theory. The calculated diffusivity is in excellent agreement with experiemental data. The same interatomic potntial also is used to study the formation of small clusters of oxygen atoms in silicon. The structures of these clusters are found by NPT molecular dynamics simulations, and their free energies are calculated by thermodynamic integration. These free energies are used to predict the temperature dependence of the equilibrium partitioning of oxygen into clusters of different sizes. The calculations show that, for given total oxygen concentration, most oxygen atoms are in clusters at temperature below 1300K, and that the average cluster size increases with decreasing temperature. These results are in qualitative agreement with effects of thermal annealing on oxygen precipitation in silicon crystals.

mtrl-th↗